Cancer chemotherapy agents frequently introduce DNA damage and, as a consequence, trigger cell cycle arrest or apoptosis, referred to as checkpoint responses. We have developed a two-hybrid-system based yeast assay that detects increased interaction between certain checkpoint proteins following certain DNA-damaging treatments. This phenomenon accompanies checkpoint activation and can be detected by colony growth on selective medium in specially constructed strains of the yeast Saccharomyces cerevisiae. Effective cancer chemotherapy frequently relies on a combination of agents. This application addresses the continued need to identify small molecules that have activity against cancer cells and to characterize novel agents that amplify or modify their effect. We plan to further refine the assay conditions for large-scale robotic screening and, as a proof-of-principle study, to address a sophisticated screening goal: to isolate novel compounds that enhance (or diminish) the checkpoint-activating effect of the established chemotherapy drug camptothecin. It is expected that the usefulness of this agent class of topoisomerase I inhibitors can be enhanced by providing adjuvants that enhance its effect on tumor cells or blunt its toxicity towards normal cells. To this end, the following specific aims will be pursued: 1. To demonstrate the feasibility of developing the assay into a high- throughput screening tool, with special emphasis on screening for agents that modify the camptothecin effect. 2. To modify and test the appropriate instrumentation for demonstration of high throughput capability. 3. To screen a compound library for agents that modify the effects of camptothecin. We plan to screen the National Cancer Institute's Diversity Compound set (1,900 agents) during Phase I that is already available to us. At the successful completion of this project, we will have established and validated a unique, robust, cost efficient and rapid screening system and will have made substantial progress towards isolation of lead compounds that can be developed into amplifiers or adjuvants in camptothecin cancer chemotherapy. Effective cancer chemotherapy frequently relies on a combination of agents. This application addresses the continued need to identify small molecules that have activity against cancer cells and to characterize novel agents that amplify or modify their effect. University of North Texas Health Science Center (UNTHSC) has developed an innovative technique that detects DNA damage caused by chemotherapy agents used in cancer treatment. During this STTR project, UNTHSC will work with a local high technology company (UHV Technologies, Inc.) to further develop this technique for large-scale robotic screening to isolate novel compounds that enhance (or diminish) the effects of the established chemotherapy drug camptothecin. UHV will modify its high throughput cancer drug discovery system developed under previous NIH funding to implement and demonstrate this new technique by screening a compound library for agents that modify the effects of camptothecin. [unreadable] [unreadable] [unreadable]